This invention relates generally to fuel cells and, more particularly, to recovery of fluid for use by a fuel cell system.
Fuel cells electrochemically convert fuels and oxidants to electricity. A Proton Exchange Membrane (hereinafter xe2x80x9cPEMxe2x80x9d) fuel cell converts the chemical energy of fuels such as hydrogen and oxidants such as air/oxygen directly into electrical energy. The PEM is a solid polymer electrolyte that permits the passage of protons (i.e., Hxe2x88x92 ions) from the xe2x80x9canodexe2x80x9d side of a fuel cell to the xe2x80x9ccathodexe2x80x9d side of the fuel cell while preventing passage therethrough of reactant fluids (e.g., hydrogen and air/oxygen gases). The direction, from anode to cathode, of flow of protons serves as the basis for labeling an xe2x80x9canodexe2x80x9d side and a xe2x80x9ccathodexe2x80x9d side of every layer in the fuel cell, and in the fuel cell assembly or stack.
In general, an individual PEM-type fuel cell may have multiple, generally transversely extending layers assembled in a longitudinal direction. In a typical fuel cell assembly or stack, all layers which extend to the periphery of the fuel cells have holes therethrough for alignment and formation of fluid manifolds that generally service fluids for the stack. Typically, gaskets seal these holes and cooperate with the longitudinal extents of the layers for completion of the fluid supply manifolds. As may be known in the art, some of the fluid supply manifolds distribute fuel (e.g., hydrogen) and oxidant (e.g., air/oxygen) to, and remove unused fuel and oxidant as well as product water from, fluid flow plates which serve as flow field plates of each fuel cell. Other fluid supply manifolds circulate coolant (e.g., water) for cooling the fuel cell.
In a typical PEM-type fuel cell, the membrane electrode assembly (hereinafter xe2x80x9cMEAxe2x80x9d) is sandwiched between xe2x80x9canodexe2x80x9d and xe2x80x9ccathodexe2x80x9d gas diffusion layers (hereinafter xe2x80x9cGDLsxe2x80x9d) that can be formed from a resilient and conductive material such as carbon fabric or paper. The anode and cathode GDLs serve as electrochemical conductors between catalyzed sites of the PEM and the fuel (e.g., hydrogen) and oxidant (e.g., air/oxygen) which flow in respective xe2x80x9canodexe2x80x9d and xe2x80x9ccathodexe2x80x9d flow channels of respective flow field plates.
A typical fuel cell system generates condensate water at various locations within the system. Therefore, condensate traps have generally been designed and located at these locations to aid in the collection of condensate. The condensate may be collected and stored in a condensate accumulation container for future use by the system.
Whereas, it may be undesirable to allow air to escape through the condensate traps, various arrangements have been designed to prevent air from escaping through the traps. For example, a needle and float arrangement may be utilized to allow condensate to escape when present, however the escape will be plugged when there is no condensate in the trap.
It has been found that undesirable gasses may accumulate in the condensate collection container. Such gasses may become entrained or dissolved in the condensate removed in the system. The gasses may build up in the condensate collection container and present a hazard to the system. For example, a flammable gas such as hydrogen may accumulate in the condensate collection container and present a safety hazard to the system.
The present invention provides a method for recovering fluid from a fuel cell system. The method includes providing the fuel cell system with a fluid collection container. The fluid collection container has a gas inlet and a gas outlet. The method further includes collecting condensate from the fuel cell system then transporting the condensate to the fluid collection container. A purge gas is provided to the gas inlet, wherein the purge gas flows through the fluid collection container and exits through the gas outlet.
In another aspect, a method is provided for purging undesirable gas from a fluid container operating with a fuel cell system. The fluid container has an inlet and an outlet. The method includes providing a purge gas to the inlet. The purge gas flows through the fluid container and exits through the outlet.
In another aspect, a fluid collection system is provided for a fuel cell system. The fluid collection device includes a fluid collection container which has a gas inlet, a gas outlet, at least one fluid inlet, and a fluid outlet. The at least one fluid inlet allows condensate to enter the fluid collection container. A fluid is contained within the fluid collection container. An undesirable gas is also contained within the fluid collection container. The gas inlet allows a purge gas to enter the fluid collection container to substantially purge the undesirable gas out of the fluid collection container through the gas outlet.
In another aspect, a method is provided for operating a fuel cell system. In general, water is separated from a reactant (process) stream and the water is collected in a collection or accumulation chamber. The atmosphere of the chamber is purged either continually or periodically. The water may be filtered to maintain a desired purity, and may be heated to generate water vapor (steam). The steam may be used, for example, to humidify a fuel processor inlet reactant stream to a desired steam to carbon ratio (3:1 for example). The steam to carbon ratio may be adjusted by adjusting the temperature of the humidified stream, by adjusting the amount of steam generated, and by metering the amount of steam introduced to the process stream (as examples). In some embodiments, the steam may be generated in a steam generator downstream from the fluid collection container (also referred to as an accumulation chamber). In other embodiments, the steam may be generated within the fluid collection container. In still other embodiments, the steam may be generated within the fluid collection container, and a fuel processor reactant gas may be used as the purge gas and be humidified by the steam. Other embodiments and features are possible and within the scope of the claims presented below.